Cold Pressure Welding: Principle, Type, Advantages and Disadvantages, Equipment

Cold pressure welding is a method to realize solid state welding by plastic deformation of the metal to be welded under pressure at room temperature.

Through plastic deformation, impurities such as oxide film on the interface of the joint are extruded to make the pure metal contact closely and achieve intergranular bonding.

The common softening zone, heat affected zone and brittle metal intermediate phase of hot welded joints will not be generated.

Cold Pressure Welding: Principle, Type, Advantages and Disadvantages, Equipment 1

It is mainly used for welding metals with good plasticity (such as aluminum, copper, etc.).

Cold Welding Principle

The principle of cold pressure welding is relatively simple. Under the action of the applied pressure, the workpiece to be welded will deform greatly through the physical contact of the materials.

During deformation, the oxide film on the surface will break, and the plastic deformation of the materials will be squeezed out of the connection interface, so that pure metals will contact each other, and metal bonds will be bonded to form a solid connection joint.

When butt cold pressure welding, first put the cleaned weldment into the fixture, make the end extend a certain length, and then clamp it.

When the movable fixture moves forward, at the same time, according to the nature of the material to be welded and the size of the end face of the workpiece, pressure is applied for upsetting, so that the end face of the workpiece produces local plastic deformation, extrudes some metals and impurities.

Under the continuous action of the welding pressure, the atoms on the contact surface of the workpiece form a combination between crystals, so that the workpieces are closely connected together, forming a welding joint, and completing the cold pressure welding process.

The number of upsetting depends on different materials, generally 1~3 times.

There are two important factors to realize cold pressure welding:

First, a certain pressure is applied between the workpieces, which is a necessary condition for metal to produce local plastic deformation and atomic bonding;

Second, under the pressure, the end metal of the workpiece must have enough plastic cold pressure, which is a sufficient condition for welding.

If cold pressure welding is carried out in the closed mold cavity, the applied pressure is greater.

Because the metal cannot have enough plastic cold pressure, cold pressure welding will not be realized.

In addition, in some cases, it is not enough to rely only on pressure and plastic deformation.

There are four factors: pressure, sufficient plastic deformation, temperature generated by plastic deformation time and atomic diffusion.

In order to carry out cold pressure welding smoothly, it is required that the metal to be welded should have great plasticity at low temperature, so it is difficult to carry out cold pressure welding for metal materials with higher hardness.

Cold Welding Type

Cold Pressure Welding: Principle, Type, Advantages and Disadvantages, Equipment 2

According to the different forms of cold pressure welding joint, it can be divided into lap cold pressure welding and butt cold pressure welding.

(1) Lap cold pressure welding

When lapping cold pressure welding, the workpiece shall be lapped and placed, and then the steel indenter shall be used for pressurization.

When the indenter is pressed into the necessary depth, the welding shall be completed.

Lap cold pressure welding is also divided into lap spot welding and lap seam welding.

The welding spot formed by columnar indenter is called cold press lap spot welding;

The welding seam formed by roller type indenter is called cold press lap seam welding.

Lap seam welding is divided into rolling welding, sleeve welding and extrusion welding.

Lap cold pressure welding is mainly used for the connection of foil and plate.

(2) Butt cold pressure welding

During butt cold pressure welding, clamp the workpiece at the left and right jaws respectively, extend a certain length, apply sufficient upset pressure to make the extended part produce radial plastic deformation, extrude the impurities on the welding surface to form metal flash, and the closely contacted pure metal forms weld, completing the welding process.

Butt cold pressure welding is mainly used to manufacture butt joints of the same or different metal wires, bars or pipes.

Cold Welding Equipment

Cold Pressure Welding: Principle, Type, Advantages and Disadvantages, Equipment 3

Cold pressure welding equipment mainly refers to cold pressure welding tongs and cold pressure welding machines.

Cold pressure welding tongs are mainly used for butt cold pressure welding.

Manual cold pressure welding is suitable for field installation.

It can weld aluminum conductors with a diameter of 1.2~2.3 mm in the west.

It is widely used in welding cable plants.

Cold pressure welding mainly includes butt welding and spot welding, among which the cold pressure butt welding machine is widely used.

The cold press butt welding machine is composed of a frame, a machine head, a feeding mechanism, a scissors device, etc.

In communication, power cable and small transformer plants, large cross-section weldments are mostly connected by cold pressure welding machine.

The structure size of cold pressure welding die has a great influence on the welding pressure, which is crucial for the designer of cold pressure welding machine.

However, for users of cold pressure welding machine, as long as the cold pressure welding equipment is finalized for production, the structure size of the die will also be finalized.

The welding pressure can be selected according to the technical parameters of the welding machine.

Cold Welding Characteristic

Cold Pressure Welding: Principle, Type, Advantages and Disadvantages, Equipment 4

Advantages

Welding wire, flux and other welding materials need not be added during welding.

As the welding is carried out at room temperature, no heating device is required, the welding cost is low, the structure is simple, a large amount of electric energy can be saved, and the auxiliary time required for welding heating can be saved.

No flux is used, the joint does not need to be cleaned after welding, and there is no corrosion problem caused by flux during the use of the joint.

The welding parameters are determined by the size of the mold.

It is not necessary to adjust the current, voltage, welding speed and other parameters like arc welding.

It is easy to operate and realize automatic welding.

Dissimilar metals, whether they are miscible or not, can be cold pressed.

There is no welding heat affected zone on the joint, and there will be no softening zone and brittle metal intermediate phase.

Therefore, the electrical conductivity and corrosion resistance of the joint are excellent.

As the welding process produces deformation hardening, the joint strength of the same metal welding is not lower than the strength of the base metal, while the strength of the dissimilar metal joint is not lower than the strength of the metal with lower strength.

There is no obvious diffusion on the joint surface, which is a kind of intergranular bonding.

The characteristics of the connected metal do not affect the cold pressure welding process.

The welding quality is stable and not affected by the fluctuation of power grid voltage.

It has good working and sanitary conditions.

Disadvantages

The local deformation of cold pressure welding is large, and the lap joint has pressure pits.

For some dissimilar metals, such as Cu and Al, the weld formed after welding will produce brittle compounds due to diffusion at high temperatures, which will significantly reduce their plasticity and conductivity.

Cold pressure welding joints of such metal combinations can only work at lower temperatures.

Due to the limitation of welding machine tonnage, the lap plate thickness and butt joint section of cold pressing welding parts cannot be too large.

The hardness of the workpiece is also limited by the mold material and cannot be too high.

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